1. Field of the Invention
The present invention relates to non-impact printing using printheads of the type having multiple recording elements and more specifically to driver ICs on such printheads having circuitry for controlling current to the recording elements.
2. Description of the Prior Art
In the prior art of non-impact printing, it has been conventional to provide a printhead having a plurality of recording elements arranged in one or more rows along the length of the printhead. As an example, an LED (light-emitting diode) printhead may have several thousand LEDs arranged along the length of the printhead so that the printhead may remain stationary as a recording member such as photoconductive member in the form of a web or drum or other photosensitive medium is advanced past the printhead in a direction perpendicular to the row. The LEDs are selectively activated in accordance with data signals sent to driver circuitry and such selective activation results in recording of a latent image that may be developed. Because it is difficult to obtain a significant yield of arrays having several thousand LEDs in a row that are of acceptable light output it has become conventional to assemble on a printhead a series of LED arrays or chips each having say 128 LEDs at a resolution of, for example, 400 dots per inch (dpi). Typically, on each of opposite sides of each LED array there will be provided a driver chip IC (integrated circuit) so that one driver chip is connected to the LED array for driving the even-numbered LEDs and the other driver IC chip is connected to the LED array for driving the odd-numbered LEDs. Thus, in this example one driver IC chip may have 64 current channels that are each connected to a respective LED. The driver IC chip includes data registers for storing image data in the form of at least one binary bit per pixel to be recorded by the LED. In response to this image data, the LED may be enabled for a predetermined time period determined by a clock signal or in the case of a grey level or other multibit printer, a pixel is recorded in accordance with the data and an exposure clock determines an on-time for the LED for recording the pixel. Alternatively, recording may be by control of intensity for a fixed or variable period of time. The driver IC chip in addition to data registers and clocking means will have a separate driver channel that is dedicated for delivering a current to a particular LED to which the driver channel is connected. Another printhead may be comprised of LED arrays of 300 dpi. This printhead will have the LED arrays connected to driver chips also as above. However, in the case of the latter printhead, there is likely to be only 96 LEDs on each LED array on this printhead and such requires a driver IC chip with only 48 driver channels. The reason that the latter LED arrays have 96 LEDs is that for a printhead manufacturer to provide printheads with different resolutions, it is desirable to have assembly apparatus or other parts that can be used with either the 300 dpi or the 400 dpi arrays. It will be appreciated for the examples provided that the 300 dpi arrays and 400 dpi arrays are preferably made about the same length to facilitate use with the same assembly machines.
A problem with the prior art is that while some assembly apparatus and parts may be used with printheads of different resolutions, the driver IC chips used are specific for each resolution. Thus, the printhead with 400 dpi arrays will have driver chips with 64 driver channels each while the 300 dpi arrays will have the other driver chips with 48 driver channels.
It is an object of the invention to provide a printhead having driver IC chips that may be used with different resolutions of recording element arrays. It is a further object of the invention to provide such driver IC chips with a programmable feature allowing control of the resolution in accordance with signals sent to the driver chips.